While the burning of a candle might appear to be simple and uninvolved, the process that takes place in the burning of a candle has been described, in fact, as a process that imposes rather stringent requirements upon the candle body material, U.S. Pat. Nos. 5,578,089, 3,819,342, 3,645,705 and 3,615,289. This is illustrated, in particular, with respect to the actual burning of the candle when the heat of the candle's flame melts a small pool of the candle body material around the base of the exposed portion of the wick. This molten material is then drawn up through and along the wick by capillary action to fuel the flame. A candle's melting point is, therefore, important in that the candle material should liquefy at or below temperatures to which the candle's material can be raised by radiant heat from the candle flame. If the candle's melting temperature is too low, the candle will drip or, in an extreme case, the entire candle body will melt, dropping the wick into a pool of molten body material, with the potential that the surface of the pool could ignite. If too high a temperature is required to melt the body material, the flame will be starved because insufficient fuel will be drawn up through the wick, with the result that the flame will be too small to maintain itself. Moreover, when molten, the candle body material preferably has a relatively low viscosity to insure that it will be capable of being drawn up through the wick by capillary action. In addition to meeting the above requirements, it is preferred that the candle body material burn with a flame that is both luminous and smokeless, and that the odors produced by its combustion should not be unpleasant or intrusive.
The desire to make candles that are transparent or clear places still further demands on these already stringent requirements. The terms "clear" and "transparent" are used interchangeably herein and connote a substantial absence of cloudiness or obscurity, so that the body of the candle features an ability to let light pass through in a substantially unobstructed manner, and an ability to have coloring agent added to the composition without causing cloudiness or reducing the candle's ability to let light pass through in a relatively unobstructed manner. Preferably, the composition has a degree of clarity comparable to window glass, clear glassware, or water.
To add yet one more demand on transparent candle compositions, it would also be desirable if the transparent candles could be used as a fragrance carrier for dispersing selected fragrances, such as fragrances having a pleasant odor, or fragrances that repel insects.
Moreover, it is desirable to accelerate the cooling of candles during manufacture, for example by passing the candles through a cooling tunnel, to reduce the manufacturing time. Also, a mold release, such as a silicone based formulation, is typically used to facilitate the release of a candle from a mold during manufacture.
Transparent compositions used to make transparent candles typically have one or more undesirable characteristics. In particular, such compositions typically do not have enough rigidity to form a self-supporting candle, and require some type of container or external support. Such compositions also typically lack hardness, which may lead to an undesirable gelatinous feeling. In addition, such compositions may darken or smoke during burning, which is aesthetically undesirable. Candles made from transparent compositions may also exhibit external cracking and/or internal fractures if they are passed through a cooling tunnel during manufacture, and may also crack during burning. Also, mold release formulations generally leaves a residue that may dull the clarity of a transparent candle.
Known transparent candle compositions which are comprised of a thermoplastic polyamide resin and a flammable solvent for solubilizing the resin, such as described in U.S. Pat. Nos. 3,615,289 and 3,819,342 are vulnerable to auto-ignition, and tend to sweat, produce black smoke, and darken during burning. Sweating is the process whereby oils migrate out of the candle body to the surface, giving it an oily texture, and is most commonly caused by syneresis. Syneresis occurs whenever oil is physically squeezed out from the candle body because of excessive chemical cross linking. Sweating is not only an aesthetic drawback, but can be a performance or safety problem as well. If a candle sweats, the oil on the surface is available to ignite, which can result in an uncontrolled or torch-like situation rather than a candle.
U.S. Pat. No. 5,578,089 describes a heterophase thermally reversible mineral oil gel formed by a system of physically crosslinked block copolymers which purportedly overcome the problem of sweating and syneresis by adjusting the ratio of diblock and triblock polymers so as to ensure that all the oil remains entrained within a system of physically crosslinked copolymers. The thermoplastic rubber type polymers of U.S. Pat. No. 5,578,089 consist of block segments of styrene monomer units and rubber monomer units, wherein each block segment may consist of 100 monomer units or more (col. 7, lines 4-20). While such compositions are alleged to provide an improvement over the prior art transparent candle compositions, styrene/rubber-based candle compositions are susceptible to surface ignition, which may produce black smoke, and also have limited fragrance throw.
It would be desirable to have transparent and odorless compositions that could be used to prepare self-supporting transparent candles that do not have a gelatinous feeling. It would also be desirable to have compositions that can be used to make self-supporting transparent candles that have an aesthetically attractive appearance and that can burn safely and cleanly, without cracking or fracturing. It would also be desirable if fragrances could be readily dissolved in the composition without causing cloudiness or hazing. It would be desirable to have compositions that can be cooled during manufacture from a liquid state to room temperature in a cooling tunnel, without cracking or fracturing. In addition, it would be desirable to have compositions that shrink during cooling to the point that the transparent candle can be removed from the mold without the use of a mold release.
The present invention is directed toward self-supporting transparent candle compositions that provide these advantages while not being handicapped with the above-noted disadvantages.